Two teenagers accused in a random "thrill kill" that left a 23-year-old college athlete from Australia dead pleaded not guilty Thursday to first-degree murder charges, an Oklahoma district attorney said.

Chancey Allen Luna, 16, and Michael Dewayne Jones, 18, entered the pleas at their arraignment Thursday inside of a Stephens County courthouse, said Jason Hicks, the district attorney serving that area.

Hicks couldn't offer more details of what transpired inside the courtroom or the case because of a gag order.

Among those in attendance was Sarah Harper, the girlfriend of the victim, Christopher Lane.

Police say the teenagers shot Lane -- who was attending East Central University on a baseball scholarship -- last August as he was jogging in Duncan, a town of about 23,000 people located some 80 miles southwest of Oklahoma City.

James Edwards Jr, Chancey Luna and Michael Jones were charged in the death of Christopher Lane.

Luna, Jones and a third teenager -- James Francis Edwards, Jr. -- saw Lane passing by and shot him because "they had nothing to do," according to authorities.

As the teenagers sped away, Duncan police Chief Danny Ford told CNN affiliate KSWO that "there were some people that saw (Lane) stagger across the road, go to a kneeling position and collapse on the side of the road."

When police arrested the teens, one of them offered a motive that made clear that Lane was chosen at random.

"He said the motive was, 'We were going to kill somebody,'" Ford told Australian radio station 3AW.

After their arrest, all three alleged assailants were charged as adults, according to Kaylee Chandler, the Stephens County Court Clerk.

The shooting shook many around the college town like Sam Malchar, who called his classmate and teammate Lane "a charming guy, genuinely good person, with great character and ... a love for life."

It also reverberated some 10,000 miles away in Lane's native Australia, from which some called for a U.S. tourism boycott. Former Australian Deputy Prime Minister Tim Fischer characterized the slaying as "another example of murder mayhem on Main Street."

A judge on Thursday set Luna and Jones' trial date for August 18, which is when a jury term starts.

The other implicated teen, Edwards, is scheduled to be in court for a preliminary hearing on May 13.

Edwards' older sister, Rachel Padilla, told CNN last summer that her brother had been in trouble with police before for fighting, but was not a vicious person, and she never thought he might kill someone.